Transistor indicator circuit



Nov. 27, 1956 J. c. LOGUE ETAL 2,772,410

TRANSISTOR INDICATOR CIRCUIT Filed Sept. 30, 1954 1 5 Sheets-Sheet 1FIG. 1

ATTORNEY Nov. 27, 1956 J c, LOGUE ETAL 2,772,410

TRANSISTOR INDICATOR CIRCUIT Filed Sept. 30, 1954 .5 Sheets-Sheet 2 24l5e I5 I5c 1 FIG.4A I i E l 25e i I I 26 25b I 1 25 E g 22 y 250 I I\%v| I T? I i l ...1

VI V2 INVENTORS JOSEPH c. LOGUE BY ROBERT A. HENLE ATTORNEY UnitedStates Patent TRANSISTOR INDICATOR CIRCUIT Joseph C. Logue, Kingston,and Robert A. Henle, Hyde Park, N. Y., assignors to InternationalBusiness Machines Corporation, New York, N..Y., a corporation of NewYork Application September 30, 1954, Serial No. 459,289

12 Claims. (Cl. 340-252) This invention relates to transistor circuitsfor controlling or driving visual signals or indicators to indicateelectrical conditions in the transistor circuits.

One of the advantages of using transistor circuits, as opposed to vacuumtube circuits, is the fact that the transistor circuits operate at lowerpower levels. Furthermore, in the case of junction transistors, thecircuits operate at low potential levels. The low powers and lowpotentials involved are not sufficient to operate the presentcommercially available electrical signal devices, such as lamps. Amongthe commercially available signal lamps those with the lowest power andvoltage characteristics are neon glow lamps. Even these can not besuccessfully operated at the power and voltage levels available inconventional junction transistor circuits. Furthermore, the use in aconventional junction transistor circuit, of a potential high enough tooperate a neon glow lamp, might subject the transistor to a potentialhigh enough to damage it.

An object of the present invention is to provide an in-. dicator:circuit for operating a visual signal device in accordance with anelectrical condition in a transistor.

Another object is to provide a circuit for operating a neon glow lampunder the control of a junction transistor, without subjecting thetransistor to unduly high potentials.

A further object is to provide a transistor indicator circuit of thetype described which will also serve as a clamp for the output of atrigger.

The foregoing objects of the invention are attained by connecting to theconventional output electrode of a transistor a conventional load branchand including a load resistor and a load supply battery in series, and asecond branch including a glow discharge lamp and a second batteryconnected in series. The arrangement is such that the circuit throughthe glow discharge lamp includes in series the load resistor of thetransistor, the load supply battery and the second battery. The twobatteries are in series aiding in the lamp circuit and their totalpotential is greater than the ignition potential of the lamp. Thepotential drop cross the load resistor when the transistor is conductingis sufi'icient to reduce the potential available at the lamp terminalsbelow the discharge maintaining potential of the lamp. Consequently thelamp is lit when the transistor is off and is extinguished when thetransis' tor is on.

In one modification of the invention, the indicator driving transistoris coupled to the output of a transistor trigger circuit through acurrent limiting resistor.

In another modification of the invention, the indicator drivingtransistor is coupled directly to the output electrode of a transistortrigger circuit, and the third electrode of the transistor is suppliedwith a clamping potential which effectively limits the potential at theoutput electrode of the trigger transistor when the trigger is oif.

Other objects and advantages of the invention will become apparent froma consideration of the following specification and claims, takentogether with the accompanying drawings.

In the drawings:

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Figure 1 is a wiring diagram of an indicator circuit embodying theinvention.

Fig. 2 is a wiring diagram of a modification of the circuit of Fig. 1.

Fig. 3 is a wiring diagram of a somewhat different embodiment of theinvention.

Fig. 3a is a fragmentary wiring diagram showing other modifications ofthe circuit of Fig. 3.

Figs. 4, 4a, 5, 6 and 7 are wiring diagrams showing other modificationsof the invention.

Figure 1 There is shown in Fig. 1 an indicator driving transistorcircuit including a PNP junction transistor 1 having an emitterelectrode 12, a base electrode 1b and a collector electrode 1c.Connected between the collector electrode 10 and a ground wire 2 is aconventional load circuit including a load resistor 3 'and a load supplybattery 4. Connected between the emitter 1e and the ground wire 2 is abiasing circuit including a resistor 5 and a battery 6. Connectedbetween base electrode 1b and ground wire 2, is a battery 7.

Emitter 1e is connected through a coupling resistor 8 to the outputcircuit of a transistor trigger circuit generally indicated by thereference numeral 9. The particular type of transistor trigger circuitis not important with respect to the present invention. For example, itmay be one of the trigger circuits disclosed in the copendingapplication of Robert A. Henle et al., Ser. No. 459,381 filed September30, l954.

As indicated in Fig. l, the trigger circuit 9 includes a PNP junctiontransistor 10 having an emitter electrode 102, a base electrode 10b anda collector electrode 100. The emitter electrode 102 is grounded. Thecollector is connected through a conventional load resistor 11 and abattery 12 to ground.

A neon glow discharge lamp 13 is connected in series with a battery 14between the collector electrode 10 and ground.

Operation of Figure 1 When the transistor 10 in the trigger circuit 9 isoff, the emitter 1e is substantially at the potential of collector 100,which is then at substantially the potential or" the negative terminalof battery 12, so that emitter 1e is negative with respect to base 1b.Transistor 1 is then off, and substantially no current is flowingthrough the collector electrode 16.

The lamp 13 is connected in a series circuit including resistor 3 andthe batteries 4 and 14. The potentials of these batteries are arrangedto aid one another in this series circuit. The sum of the potentials ofbatteries 4 and 14 is greater than the breakdown or ignition po tentialof the lamp 13, so that the lamp is lit.

Assuming now that the trigger circuit 9 switches to its on condition, sothat a substantial current flows through resistor 11 and battery 12.This changes the potential of collector electrode 10c in a positivesense, and this change is transmitted through the resistor 8 to emitterelectrode 12 of transistor 1, swinging emitter 1e positive and turningtransistor 1 on and sending a substantial current through collectorelectrode 10, load resistor 3 and battery 4. This current produces apotential drop across resistor 3 which reduces the potential availableacross the terminals of the lamp 13. The value of resistor 3 is selectedso that this potential drop is sufficient to reduce the potential atlamp 13 below the discharge maintaining potential of that lamp, and thelamp is extinguished.

It may, therefore, be seen that lamp 13 indicates the condition of thetrigger circuit 9. When the lamp 13 is lit, the transistor 10 is off andwhen the lamp 13 is extinguished, the transistor 10 is on.

The resistor S in the circuit of Fig. 1 must be selected with some care.It must have sufficiently high resistance so that it will not undulyload the transistor lit, and it must have a sufiiciently low resistanceso that it will transmit sufiicient current through emitter electrode 12to produce a substantial current output from collector emitter 1c.

The circuit illustrated in Fig. 1 is not critical with respect to thecharacteristics of the lamp 1?). It is only necessary that the lamp 1?;have a discharge maintaining potential higher than that which existswhen the transistor 1 is on. The lamp 13 may have any breakdownpotential, the required potential being supplied by properly selectingthe potential of battery 1 When transistor 1 goes off, 1c goes towardthe potential of the negative terminal of battery 4 until the potentialacross the lamp 13 reaches its breakdown potential.

Figure 2 in this figure, the transistor 1 is rearranged so as to use abase input rather than art-emitter input. T he circuit elements in Fig.2 are the equivalents of-their counterparts in Fig. l and have beengiven the same reference numerals.

When the transistor is ofl, its collector 10c is at its most negativepotential, and this potential is communicated to base 1b, where it iseffective to turn the transistor 1 on. Current then flows from collector1c through resistor 3, lowering the potential at the terminals of lamp13 and extinguishing the light.

When transistor 10 turns on, its collector itic swings positive, andthis positive potential is communicated to base lb, where it iseffective to turn the transistor 1 off. This reduces the potential dropacross resistor 3 and the potential at the terminal of lamp 13 becomessuflicient to start a discharge, lighting the lamp.

Figure 3 The circuit of Fig. 3 is intended for use with transistortrigger circuits of the type which have a clamping circuit connected totheir output electrode or which may be operated with a clamping circuitconnected to their output electrode. Such a trigger circuit is shown anddescribed in the copending application of Robert A. Henle et at, SerialNo. 459,381, filed September 30, 1954. In the present circuit, theindicator driving transister performs the function of a clamp inaddition to operating the signal lamp.

The circuit of Fig. 3 includes an NPN transistor 15 having an emitterelectrode 15c, a base electrode 15b and a collector electrode 150. Thebase electrode is connected through a battery 16 to ground wire 17.Collcctor electrode 15c is connected through a load resistor and. abattery 19 to ground, and is also connected through a neon glowdischarge lamp 27 and a battery 23 to ground. Emitter 156 is connecteddirectly to an output terminal of a trigger circuit 29, which may be oneof the type disclosed in the Henle et a1. application mentioned above.The trigger circuit 2% includes a PNP junction transistor 21 having anemitter electrode 216 a base electrode 21b, and a collector electrode21c connected through a load resistor 22 and a battery 23 to ground. itis essential that the potential of battery 23 be greater than thepotential of battery 16.

Operation of Figure 3 When the transistor 21 of tri ger 21 is oil, thecollector electrode 21c tends to go to the potential of the negativeterminal of battery 23, but is clamped at the potential of the negativeterminal of battery 16, since the impedance of the transistor 15 betweenbase 15b and emitter 15a is then very low. The transistor 15 is then on,since its emitter is negative with respect to its base, and asubstantial current is flowing from collector 150 through load resistor18 and battery 19. The

the potential at its control electrode potential drop across resistor 18is suificient to lower the potential at the terminals of lamp 27 belowthe discharge maintaining potential of that lamp, and the lamp isextinguished.

When the transistor 21 turns on, the potential of electrode 210 changesin a positive sense. This change is transmitted to emitter electrode15c, thereby turning the transistor 15 oil, and reducing the currentflow through resistor 18 to a point where the potential applied to theterminals of lamp 27 is greater than its breakdown potential, therebyilluminating'the lamp.

When the transistor 21 is turned on, it may be that there is stored inthe base P-section of transistor 15 a sufficient number of minoritycurrent carriers, i. e., electrons so that the impedance between emitterelectrode 15c and base electrode 15b is momentarily lowered untilsufficient current passes through the transistor to recombine most ofthese electrons with holes. It may therefore happen that the transistor15 will apply a momentary heavy load to the transistor 21 which isundesirable. This momentary heavy load may be prevented by connecting adiode 24 in series with the emitter electrode 15c as illustrated in Fig.3a. The diode 24 will have substantially no-efl'ect on the operation ofthe circuit when the transistor 15 is on and will prevent undue loadingof transistor 21 because of minority carrier storage in the transistor15.

Figure 4 This figure is a modification of the circuit of Fig. 3 in whicha PNP transistor 25 is used instead of the NPN transistor 15 of Fig. 3.Transistor 25 is connected with a base input rather than the emitterinput of Fig. 3.

When transistor 21 is off, its collector is at its most negative value.The collector 21c tends to go to the potential of the negative terminalof battery 23, which is more negative than the negative terminal ofbattery 16. When the potential of collector 21c becomes more negativethan the negative terminal of battery 16, then current flows fromemitter ZSe through base 25b, effectively clamping collector 210 at thepotential of the nega tive terminal of battery 16. Transistor 25 is thensubstantially conductive. The current flowing from collector 25cproduces a potential drop across resistor 18 sufiicient to lower thepotential at the terminals of lamp 27 and turn out the light.

When transistor 21 turns on, its collector 21c swings positive. Thispositive potential is communicated to base 25b, Where it is effective toturn the transistor 25 011?. The potential drop across resistor 18 isthen reduced sufliciently so that lamp 27 is turned on.

Fig. 4a shows the connection of a diode 26 in series with the base oftransistor 25 in order to prevent undue loading of the trigger circuit20 by minority carrier storage in the transistor 25. This arrangementand its operation is analogous to the diode 24 of Fig. 3a in itsoperation, and no further description is considered necessary.

Figures 5 and 6 These figures show modifications of the circuits ofFigs. 1 and 2, which are adapted to use an NPN junction transistor 30 inplace of the PNP junction transistor 1 of Figs. 1 and 2.

The differences between the circuits of Figs. 5 and 6 and those of Figs.1 and 2 are those which would readily occur to one skilled in thetransistor art in shifting from one type transistor to the other.Specifically, the polarities of the batteries 4, 6 and 14 are reversedin Figs. 5 and 6 from the polarities indicated in Figs. 1 and 2.Furthermore, the biasing battery 7 of ig. 1 has been omitted from thecircuit of Fig. 5. Also, the same biasing battery has been included inthe circuit of Fig. 6, but was not used in the circuit of Fig. 2.

The operation of the circuit of Figs. 5 and 6 is analogous to that ofthe circuits of Figs. 1 and 2, and further description is believed to beunnecessary.

Figure 7 This figure illustrates a modification of the circuit of Fig.3, in which two neon glow lamps 27 are controlled by the same transistorcircuit. When using two lamps in this manner, it is necessary to add tworesistors 31, one in series with each of the two glow lamps 27. Theseresistors are added to ensure that when one lamp comes on, the potentialof the collector 15 remains sufficiently positive so that the potentialacross the second neon lamp remains greater than its ignition potential,thereby ensuring that both lamps will light, even though one lightssomewhat more quickly than the other.

Following similar principles, it is possible to use any number of neonlamps. It is only necessary that a resistor be added in series with eachof them, and that the resistors be so chosen that when all but one ofthe lamps are lighted, the dark lamp has across it a potential greaterthan its ignition potential.

Additional lamps may be inserted in the circuits of Figs. 1, 2 and 4 to6, in a manner similar to that in which the lamp 27 was inserted in thecircuit of Fig. 3 to produce the circuit of Fig. 7.

The following table shows by way of example particular values for thepotentials of the various batteries and for the impedances of thevarious resistors and capacitors, in circuits which have been operatedsuccessfully. In some cases, the values are also shown in the drawing.These values are set forth by way of example only, and the invention isnot limited to them nor to any of them. The diodes are considered tohave substantially no impedance in their forward direction andsubstantially infinite impedance in the reverse direction.

TABLE I Resistor 3 125K Battery 4 45v. Resistor 5 390K Battery 6 45v.Battery 7 5v. Resistor 8 8.1K Resistor 11 1K Battery 12 5v. Lamp 13Battery 14 45v. Battery 16 5v. Resistor 18 39K Battery 19 45v. Resistor22 3K Battery 23 15v. Lamp 27 Battery 28 45v.

1 Neon Indicator ignition voltage of 75 volts extinction voltage of 55volts.

9 Neon Indicator same as Lamp 13.

While we have shown and described certain preferred embodiments of ourinvention other modifications will readily occur to those skilled in theart, and we therefore intend our invention to be limited only by theappended claims.

What is claimed is:

1. Visual signal apparatus comprising a glow discharge lamp, anenergizing circuit for said lamp including a resistor and a source ofunidirectional electrical energy in series, said source having apotential greater than the ignition potential of the lamp, and means forcontrolling the potential across the lamp including circuit means forconducting a current through said resistor to produce a potential dropthereacross of a polarity and magnitude efiective to reduce thepotential available at the lamp below the potential required to maintaina discharge through the lamp, said circuit means comprising 'atransistorhaving a base electrode, an emitter electrode and a collector electrode,means connecting the collector elec'-- trode in series with saidresistor and at least a portion of said source of energy, and means forimpressing across the other electrodes of the transistor a signalpotential eifective to control the current flow through said collectorelectrode.

2. Visual signal apparatus, comprising a transistor having an outputelectrode, load circuit means connected to said output electrodeincluding a load resistor and a first source of unidirectionalelectrical energy in series, means for indicating an electricalcondition in said load circuit means comprising a glow discharge lamp,and an energizing circuit for said lamp including in series said loadresistor, said lamp and a second source of unidirectional electricalenergy having a polarity opposite to that of the potential drop acrosssaid resistor produced by the current flowing through said outputelectrode.

3. Visual signal apparatus as defined in claim 2, in which said firstsource of energy supplies the load circuit of said transistor and saidglow discharge lamp and said second source of energy supplies only thelamp.

4. Visual signal apparatus as defined in claim 2, in which saidindicating means includes a plurality of glow discharge lamps, aplurality of said second resistors, and a corresponding plurality ofenergizing circuits for said lamps, each said energizing circuitincluding in series a second resistor, one of said lamps, and one ofsaid second sources of unidirectional energy.

5. Apparatus for visually indicating an electrical condition,comprising: a transistor trigger circuit shiftable between two stableoutput states and including a first transistor having an outputelectrode, a load resistor and a first source of unidirectionalelectrical energy connected in series to said output electrode; meansfor amplifying an electrical condition in said trigger circuitcomprising a second transistor having a base electrode, an emitterelectrode, and a collector electrode, two of the electrodes of saidsecond transistor serving respectively as input and output electrodes, acoupling resistor connecting the output electrode of said firsttransistor and the input electrode of the second transistor, meansbiasing said input electrode in a sense to hold said second transistorin a first predetermined conductive state, said trigger circuit and saidcoupling resistor being effective when the trigger shifts from oneoutput state to the other to shift the second transistor to a secondpredetermined conductive state different from said first state, a loadresistor and a second source of unidirectional electrical energyconnected in series to said second transistor output electrode; a glowlamp and a third source of electrical energy connected in series to saidsecond transistor output electrode, said second and third sources havingterminals of opposite polarity connected, said second and third sourcesin series having a potential greater than the ignition potential of saidglow lamp, said second transistor being eifective when in one only ofsaid first and second conductive states to produce across said loadresistor a potential drop sufiicient to reduce the potential at the glowlamp terminals below its discharge maintaining potential.

6. Apparatus for indicating an electrical condition as defined in claim5, in which the emitter electrode of the second transistor serves as aninput electrode.

7. Apparatus for indicating an electrical condition as defined in claim5, in which the base electrode of said second transistor serves as theinput electrode.

8. Apparatus for visually indicating an electrical condition,comprising: a transistor trigger circuit including a first transistorhaving an output electrode, a resistor and a first source ofunidirectional electrical energy connected in series to said outputelectrode; means for amplifying an electrical condition in said triggercircuit comprising a second transistor having a base electrode, anemitter electrode, and a collector electrode, two of the electrodes ofsaid second transistor serving respectively as input and outputelectrodes, means directly connecting the output electrode of said firsttransistor and the input electrode of the second transistor, meansbiasing the third electrode of the second transistor in a sense to holdsaid second transistor ON when said first transistor is OFF, saidbiasing means comprising'a second source of electrical energy having apotential smaller than said first source and means connecting to saidthird electrode a terminal of said second source whose polaritycorresponds to that of the terminal of said first source connected tosaid input electrode, said second source being effective when said firsttransistor is OFF to clamp the output potential thereof, a load resistorand a second source of unidirectional electrical energy connected inseries to said output electrode, a glow lamp and a third source ofelectrical energy connected in series to said out-put electrode, saidsecond and third sources having terminals of opposite polarityconnected, said second and third sources in series having a potentialgreater than the ignition potential of said glow lamp, said secondtransistor being effective when conducting to produce across said loadresistor a potential drop suflicient to reduce the potential at the glowlamp terminals below its discharge maintaining potential.

9. Apparatus for indicating an electrical condition as defined in claim8, in which said second transistor is an NPN transistor and the emitterelectrode thereof serves as the input electrode.

10. Apparatus for indicating an electrical condition as defined in claim8, in which said second transistor is a PNP transistor and the baseelectrode thereof serves as an input electrode.

11. Apparatus for indicating an electrical condition as defined in claim8, in which said directly connecting means includes a diode poled toprevent undue loading of the first transistor by minority carrierstorage in the second transistor.

12. A transistor circuit including a first transistor having an outputelectrode, a resistor and a first source of unidirectional electricalenergy connected in series to said output electrode, means for clampingsaid output electrode to limit the potential thereof when said firsttransistor is OFF, said clamping means comprising a second transistorhaving an input electrode connected to the output electrode of saidfirst transistor and a second electrode connected to a source ofclamping potential.

References Cited in the file of this patent UNITED STATES PATENTS2,547,386 Gray Apr. 3, 1951 2,665,845 Trent Jan. 12, 1954 2,696,739Endres Dec. 14, 1954

